Parent-Only Financial Information - Condensed Statements of Cash Flows (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 33,064,000	$ (4,926,000)	$ 18,638,000	$ 16,533,000	$ 23,450,000	$ 24,971,000	$ 18,980,000	$ 21,173,000	$ 63,309,000	$ 88,574,000	$ 71,932,000
Net gain on sales of investment securities									8,278,000	16,000	668,000
Amortization of deferred costs on borrowings										0
Net amortization of purchase accounting adjustments									(21,557,000)	(14,094,000)	(16,733,000)
Net cash provided by operating activities									132,656,000	100,247,000	92,551,000
Cash flows from investing activities:
Net cash (used in) provided by investing activities									(22,169,000)	(172,122,000)	48,553,000
Cash flows from financing activities:
Net proceeds from issuance of subordinated notes									122,180,000	0	0
Repayments of other borrowings									(8,109,000)	(263,000)	(439,000)
Dividends paid									(42,917,000)	(34,241,000)	(29,564,000)
Purchase of treasury stock									(14,814,000)	(26,066,000)	(10,837,000)
Net proceeds from the issuance of preferred stock									55,529,000	0	0
Exercise of stock options									1,241,000	1,335,000	5,324,000
Net cash provided by (used in) financing activities									1,074,948,000	82,773,000	(128,389,000)
Non-cash activities:
Unsettled trades of equity securities									8,142,000	0	0
OceanFirst Financial Corp.
Cash flows from operating activities:
Net income									63,309,000	88,574,000	71,932,000
(Increase) decrease in advances to subsidiary Bank									(73,426,000)	(13,852,000)	15,262,000
Undistributed earnings of subsidiary Bank									(4,071,000)	(15,928,000)	(45,556,000)
Net gain on sales of investment securities									20,460,000	0	0
Amortization of deferred costs on borrowings									576,000	261,000	262,000
Net amortization of purchase accounting adjustments									638,000	453,000	395,000
Change in other assets and other liabilities									648,000	(184,000)	4,076,000
Net cash provided by operating activities									(32,786,000)	59,324,000	46,371,000
Proceeds from sale of investment securities									15,339,000	0	0
Cash flows from investing activities:
Purchase of investment securities									(95,228,000)	0	0
Increase in ESOP loan receivable									0	0	(8,400,000)
Repayments on ESOP loan receivable									1,200,000	1,160,000	1,020,000
Net cash (used in) provided by investing activities									(78,689,000)	1,160,000	(7,380,000)
Cash flows from financing activities:
Net proceeds from issuance of subordinated notes									122,180,000	0	0
Repayments of other borrowings									(7,999,000)	0	0
Dividends paid									(42,917,000)	(34,241,000)	(29,564,000)
Purchase of treasury stock									(14,814,000)	(26,066,000)	(10,837,000)
Net proceeds from the issuance of preferred stock									55,529,000	0	0
Exercise of stock options									1,241,000	1,335,000	5,324,000
Net cash provided by (used in) financing activities									113,220,000	(58,972,000)	(35,077,000)
Net increase in cash and due from banks									1,745,000	1,512,000	3,914,000
Cash and due from banks at beginning of year				$ 5,442,000				$ 3,930,000	5,442,000	3,930,000	16,000
Cash and due from banks at end of year	$ 7,187,000				$ 5,442,000				$ 7,187,000	$ 5,442,000	$ 3,930,000